1. Field of the Invention
The present invention relates to control valves and more particularly relates to an improved pilot control relay valve utilized to monitor pressure conditions in a pressurized system and to cause the system to shut down in response to detection of operating pressures outside of a predetermined acceptable pressure range. Accurate monitoring is provided for by dual pistioning action hydraulically actuates a visual indicator mounted on the slide valve of said control valve.
2. General Background
A control valve is normally placed in a fluid flow line or a fluid actuator to prevent the flow of fluid until a fluid pressure reaches a predetermined operating range. Control valves known in the art which have been patented include:
U.S. Pat. Nos. 3,943,974, 4,240,609, 4,074,702, 4,254,799, 4,194,529, 4,252,145, 4,194,719, 4,252,146, 4,196,740, 4,254,798, 4,203,571, 4,256,141, 4,207,924, 4,263,938, 4,213,481, 4,267,862, 4,215,746, 4,275,865, 4,217,934, 4,237,931, 4,220,174, 4,239,058, 4,234,162, 3,038,439, 3,448,228, 3,109,441, 3,202,170, 3,189,277, 3,769,996, 3,985,337, 3,035,450, and 3,401,666.
U.S. Pat. Nos. 3,943,974, 4,194,529, 4,074,702, 4,196,750, 4,207,924, 4,239,058, 4,252,145, 4,256,141 and 4,263,938 provide a single elongated housing with a bore extending longitudinally therethrough and containing a slide valve mounted therein. The slide valve and internal components of the housing are not sealed and therefore are exposed to adverse environmental influences such as mud, dirt salt water, and the like. In this regard, frequent maintenance is required on the control valve resulting in a shut down of the main line during such period. Another disadvantage of the prior art is that in using a single housing with a shaft therein to manually reset the slide valve to an outward or displaced position, the shaft itself must be grasped and pulled out, often resulting in bending of the shaft assembly. This manual reset capability increases the possibility of a complete failure of the shaft or bending to a point where it is unable to return to its normal functioning position. A further disadvantage of the prior art is that these control valves use a latching pin which provides for a manual detent means when depressed which actually engages the slide valve, and, in extended operations wears a groove therein, the groove eventually becoming rounded to a point that the detent pin begins to slip and fail in its intended function. The wearing can also lead to O-ring slippage destroying the systems integrity. Another disadvantage of prior art is that the indicator means, as with the internal components, is exposed to adverse environmental conditions by being externally mounted on the slide valve. This external mounting also leads to abuse during the manual resetting of the slide valve. Also, when the indicator is malfunctioning and needs replacement, the entire contol valve becomes inoperable and the main line it is controlling must be shut down.
A further disadvantage of the prior art is the use of a fluid passageway extending longitudinally within the slide valve to direct fluid from the pilot port to the indicator means to actuate the indicator in that the passageway can be blocked or provide an uneven pressure distribution thus resulting in a "false" indication of the operating condition of the system. The present invention provides a solid shaft longitudinal of the bore of the slide valve which is subject to fluid pressure from the pilot port to actuate the indicator means.
The present invention seeks to solve the above-named problems by providing a second external housing which protects the slide valve shaft from the effects of the environment and manual abuse by sealingly providing a cover for the internal components and a means for manually resetting the valve. The second external housing also provides a housing for the manual detent means so that it can engage the lip of the main body housing instead of the slide valve shaft itself to provide consistent gripping without wear on the slide valve shaft. Further, the indicator means is encapsulated in the secondary external housing so that it can be easily removed for maintenance or replacement while the control valve remains in operation.
Further, in considering the shortcomings of the prior art devices, it should be noted that many prior art slide valve-actuated indicators are actuated by fluid pressure and due to unequal distribution of fluid and clogging are not capable of giving consistently accurate indictions of the operating conditions of the system. The present invention, by providing a second internal shaft and piston, produces a consistent and reliable visual indication of the operating conditions of the system.